1. Field of the invention
This invention relates to electrical drive systems, especially DC drive systems. In particular it relates to brushless DC drive systems, including motors and amplifiers, of the type frequently referred to as trapezoidal drives. The invention also encompasses motors forming parts of such systems, and in addition provides certain features applicable not only to brushless DC drives but also to electric motors and drives of other kinds.
The brushless drives in question generally have an armature portion and a field structure portion, and in one form of construction, the field structure portion may be a permanent magnet rotor, having at least two poles, and the armature portion is a stator having windings which are energized in steps to advance the rotor poles and thus bring about rotation of the rotor. Particularly favoured constructions of motors of this type, often referred to as an "inside-out" construction, have six rotor poles and three phase windings.
2. Description of the prior art
Drives of this general kind are discussed in the papers "Electronically Commutated DC Feed Drives for Machine Tools" by P. Zimmermann, Motorcon September 1982 proceedings, "Ultra High Performance Brushless DC Drive" by A. C. Stone and M. G. Buckley, delivered at a conference in Brighton in October 1984, and "Novel Design and Control of Trapezoidal Back E.M.F. Motor -The Smooth Transition From Brush to Brushless DC" by A. C. Stone and M. G. Buckley, Motorcon April 1985. These papers contain extensive discussions of relevant background material in this field.